The present invention pertains to liquid storage vessels, and more particularly, to a valve assembly for venting a liquid storage vessel.
Liquids such as water, milk, and juice are stored and transported in large vessels, or tanks. To fill these tanks, air in the tank must be able to escape when the tank is filled with the liquid. To remove liquid from these tanks, air must be drawn into the tank to prevent a vacuum being created by removal of the liquid. Accordingly, a vent is provided to permit air to enter the interior of the tank. Because these vents do not include a filter, unfiltered air is necessarily drawn into the tank to effect removal of the liquid. Such unfiltered air includes airborne contaminants which are introduced to the liquid as it is removed from the tank.
One example of large volume storage vessel is the large container used for water towers which are part of public water supply systems. The container is an elevated tank having a vent for passage of air. These vents may include a screen to keep animals and large insects out (for example, a one inch mesh screen may be used). However, small insects and airborne contaminants enter through these screens, especially when unfiltered air is drawn into the tower tank as the water is discharged therefrom. Where the air includes a high level of contaminants, the contaminants may compromise the safety of the water. Typically, additional quantities of chlorine are added to the water to kill any bacteria introduced to the water by the air entering through the vent. However, it is undesirable to add additional chemicals in drinking water since these chemicals detrimentally effect the taste of the water and may present their own health risk.
Another example of such storage vessels are tank trucks which are utilized to transport milk, juice and other beverages from a source to a bottling plant. These trucks require a vent for passage of air when the tank is loaded and unloaded. Although the vent may be closed during transportation and storage; however, since the tank vents do not include a filtration system, the liquid contents will be effected by airborne contaminants entering through the vent during loading and unloading of the tank.
Accordingly, it is desirable to provide a system for decreasing the amount of contaminants drawn into a storage or transportation vessel during emptying of a tank and permitting venting during filling. It is preferable to provide such a system in a manner which avoids the necessity of adding large quantities of chemicals to the liquid. It is further desirable that the vent be provided by a relatively low cost, readily retrofittable, mechanism.